HELLLLPPP - System Problem - No POST

I was recently putting together a computer out of some older parts, plus some new ones. I purchased a brand new Asus CUSL2 MB, and attempted to get it up and running with a Cel500. First time I try to power up, no POST, but the light on the MB comes on, as well as the system fans. So I figure, dead processor or RAM. Try both components in a different computer - no problem. Next, I look to the MB for the problem, so I return it and replace it with an identical piece. And I still get the same problem. No POST, no beeps, no video, nothing!!! My last thought is, that the only common component in all of the problems is the power supply. So I replace that. Still NOTHING!!! Is there any way that a -CASE- can factor into the operation of a system? Or is there something blatantly obvious that I may have missed doing when I set this up?? Please help!

Thank you in advance